Belt-fixing type fixing devices have been known as fixing devices that are included in, for example, printers or copying machines, and that fix a toner image onto a sheet by heating the sheet. Some fixing device includes a belt, a nip member, a sliding sheet, and a fastening member. The nip member is disposed inside a loop of the belt. The sliding sheet is sandwiched between the belt and the nip member. The fastening member is disposed opposite to the belt relative to the nip member. In such a fixing device, end portions of the sliding sheet in a circumferential direction of the belt are fastened to the fastening member by elastic force of plate springs.